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Re: Placing Two Identical Regulated DC supplies in Parallel

 

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I¡¯m glad it was helpful John.

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I know there is some info out there on how to do it, and I¡¯m not saying it can¡¯t be done¡­ just really not a recommended configuration.

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I work for TDK-Lamba in NJ, where we design and manufacture our Genesys and Genesys+ supplies.? I¡¯m actually working on a new line of equipment for a customer and I literally pulled parallel kits from our assembly line yesterday to begin testing this exact configuration with both two and four parallel supplies.

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Granted, things are much smaller with fixed 12V supplies, but the principle is the same.? And even with remote sense hooked up, you risk a mis-match causing oscillation and noise as the supplies try to figure it out.? That¡¯s not what you need in a radio/repeater scenario, especially with the load constantly changing as the transmitter goes on and off during a QSO.? We have oscilloscope pictures during dynamic load testing and the voltage spikes are crazy- all that needs to be suppressed, or at least accounted for.? Switching several amps as the load changes can easily cause voltage spikes over 100V for several micro-seconds on the supply output, and if the filter caps aren¡¯t rated for that, you¡¯ll only know it happened because of the smoke and the loud bang.? (Trust me, the caps will blow to protect any fuses in the circuit.)

If you have two supplies you were planning on using, I would honestly sell them and put the money towards one supply that can handle the load plus 25-50%.? Just my 2-cents.

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Good luck!!

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73,

Marlo

KA2IRQ

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From: JOHN HASERICK <jhaserick84@...>
Sent: Saturday, April 19, 2025 8:29 AM
To: [email protected]; Marlo Montanaro - KA2IRQ <ka2irq@...>
Subject: Re: [repeater-builder] Placing Two Identical Regulated DC supplies in Parallel

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Thank you for the extensive information Marlo, and the other great replies also. It sure was tempting to do, until your reply, as these Astron SS-30 supplies have overvoltage, overcurrent, and overtemp protection, and the internal voltage sensor wires are right next to? the output terminals, which could have short low voltage drop leads between supplies.

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John

On 04/19/2025 8:13 AM EDT Marlo Montanaro - KA2IRQ <ka2irq@...> wrote:

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I work for an industrial power supply manufacturer, in the engineering dept.? This is not a recommended configuration unless the power supplies are both designed for it.

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You risk uneven load sharing which can overload one supply while the other does almost nothing.? The more heavily loaded supply could overheat or go into current limit.? This can happen with even very small voltage differences.... i.e., 12.00 vs. 12.05 volts.??

Despite the seemingly identical nature on paper, you can have large circulating currents between the supplies since there is almost no chance they will be perfectly voltage matched.? This wastes power and can damage internal components, especially if one supply is not designed to sink current.

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If they are switching supplies, you can create feedback loops where the supplies may interact in strange ways, potentially causing oscillations or unstable behavior... there is nothing syncing the switching frequencies.

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The supplies may have slightly different protection thresholds for overcurrent or overvoltage.? If one supply trips in a fault condition, that leaves the other supply to suddenly take the full load.? If you design things so one supply can take the full load to avoid this, then you really don't need two supplies.

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Supplies may power up at slightly different rates which can cause temporary overcurrent conditions.

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The supplies we manufacture are designed for parallel operation but to do this they have several sophisticated control boards, data communication between them, and very heavy duty buss bars connected between them to handle high current conditions and provide a very low resistance path between the outputs.

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73,

Marlo

KA2IRQ

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